With recent developments in information communication technology, various kinds of content including restaurant information, product information, event information, news, music, video, or electronic books have been provided for users through networks. Retrieval service including keyword or genre retrieval is provided to support users who retrieve information suitable for the users from these vast amounts of content, and recommendation service is provided for recommending content suitable for users through a system.
For extraction of the attributes of content used in the retrieval service and recommendation service, for example, a significance calculation method is proposed in Patent Literature 1 in which the degrees of significance of various attribute combinations are flexibly evaluated from the attributes of content.